Fluoride-conversion synthesis of homogeneous actinide oxide solid solutions

Abstract

Here, a novel route to synthesize (U, Th)O2 solid solutions at a relatively low temperature of 1100 °C is demonstrated. First, the separate actinide oxides reacted with ammonium bifluoride to form ammonium actinide fluorides at room temperature. Subsequently, this mixture was converted to the actinide oxide solid solution using a two-phased heat treatment, first at 610 °C in static air, then at 1100 °C in flowing argon. Solid solutions obeying Vegard’s Law were synthesized for ThO2 content from 10 to 90 wt%. Microscopy showed that the (U, Th)O2 solid solutions synthesized with this method to have considerably high crystallinity and homogeneity, suggesting the suitability of material thus synthesized for sintering into nuclear fuel pellets at low temperatures.